Multiple lockfiles error (#1228)

These changes build on top of [existing pnpm support](#1224) and modify the failure message shown when multiple lockfiles are detected to now include pnpm.

lib/failure.sh

@@ -115,53 +115,62 @@ fail_iojs_unsupported() {
 }
 
 fail_multiple_lockfiles() {
+  local build_dir="${1:-}"
   local has_modern_lockfile=false
-  if [ -f "${1:-}/yarn.lock" ] || [ -f "${1:-}/package-lock.json" ]; then
-    has_modern_lockfile=true
-  fi
 
-  if [ -f "${1:-}/yarn.lock" ] && [ -f "${1:-}/package-lock.json" ]; then
-    mcount "failures.two-lock-files"
-    meta_set "failure" "two-lock-files"
+  declare -A lockfiles=(
+    ["npm"]="package-lock.json"
+    ["pnpm"]="pnpm-lock.yaml"
+    ["Yarn"]="yarn.lock"
+  )
+
+  local detected_package_managers=()
+  for package_manager in "${!lockfiles[@]}"; do
+    lockfile="${lockfiles["$package_manager"]}"
+    if [ -f "$build_dir/$lockfile" ]; then
+      has_modern_lockfile=true
+      detected_package_managers+=("$package_manager")
+    fi
+  done
+
+  if (( "${#detected_package_managers[*]}" > 1 )); then
+    readarray -td '' package_managers_sorted < <(printf '%s\0' "${detected_package_managers[@]}" | sort -z --ignore-case)
+    mcount "failures.multiple-lock-files"
+    meta_set "failure" "multiple-lock-files"
     header "Build failed"
-    warn "Two different lockfiles found: package-lock.json and yarn.lock
+    warn "Multiple lockfiles found
 
-       Both npm and yarn have created lockfiles for this application,
-       but only one can be used to install dependencies. Installing
-       dependencies using the wrong package manager can result in missing
+       Multiple package managers ($(IFS=','; printf '%s' "${package_managers_sorted[*]}")) have created lockfiles for this application,
+       but only one can be used to install dependencies. Installing dependencies using the wrong package manager can result in missing
        packages or subtle bugs in production.
 
-       - To use npm to install your application's dependencies please delete
-         the yarn.lock file.
-
-         $ git rm yarn.lock
+       Only one of the following package manager lockfiles are supported at a time:
+       - ${lockfiles["npm"]}
+       - ${lockfiles["Yarn"]}
+       - ${lockfiles["pnpm"]}
 
-       - To use yarn to install your application's dependencies please delete
-         the package-lock.json file.
-
-         $ git rm package-lock.json
+       Please delete the lockfile(s) that should not be in use.
     " https://help.heroku.com/0KU2EM53
     fail
+
   fi
 
   if $has_modern_lockfile && [ -f "${1:-}/npm-shrinkwrap.json" ]; then
     mcount "failures.shrinkwrap-lock-file-conflict"
     meta_set "failure" "shrinkwrap-lock-file-conflict"
     header "Build failed"
-    warn "Two different lockfiles found
+    warn "Multiple lockfiles conflicting with npm-shrinkwrap.json
 
-       Your application has two lockfiles defined, but only one can be used
+       Your application has multiple lockfiles defined which conflicts with the
+       shrinkwrap file you've been using. Only one lockfile can be used
        to install dependencies. Installing dependencies using the wrong lockfile
        can result in missing packages or subtle bugs in production.
 
-       It's most likely that you recently installed yarn which has its own
-       lockfile by default, which conflicts with the shrinkwrap file you've been
-       using.
-
        Please make sure there is only one of the following files in your
        application directory:
 
        - yarn.lock
+       - pnpm-lock.yaml
        - package-lock.json
        - npm-shrinkwrap.json
     " https://help.heroku.com/0KU2EM53

test/fixtures/yarn-pnpm-and-npm-lockfiles/package.json

@@ -0,0 +1,9 @@
+{
+  "name": "yarn",
+  "version": "1.0.0",
+  "main": "index.js",
+  "license": "MIT",
+  "dependencies": {
+    "lodash": "^4.16.4"
+  }
+}